Commercial glucoamylase immobilizes very slowly on highly activated glyoxyl-agarose supports. The resulting derivatives were only 6-fold more stable than soluble enzyme. The unmodified glucoamylase, highly glycosylated, seems to have a low number of Lys able to react with glyoxyl groups on the support. Thus, the enzyme surface was highly enriched in amino groups by chemical modification of carboxyl groups (activated with carbodiimide) with ethylenediamine. The aminated enzyme preserves a good percentage of activity (80%) and it exhibits the same stability than unmodified enzyme. The aminated enzyme was immobilized very rapidly on highly activated glyoxyl-agarose support. The new resulting derivatives preserved 50% of activity and were more than 500-fold more stable than soluble enzyme in experiments of thermal inactivation. (C) 2010 Elsevier Ltd. All rights reserved.